Fiber optics are increasing being utilized for communicating wide band widths of data at high data transmission rates. Based upon the material and labor costs associated with producing a fiber optic simplex cable, the use of fiber optics typically becomes cost efficient (i.e., as compared to conventional metallic cable) when the data rates exceed about 100,000 bits per second (bps). Today, the applications for fiber optics are typically limited to telecommunications, cable television, and highly advanced aircraft/spacecraft. With respect to the latter, fiber optics are used extensively in the Boeing/Sikorsky RAH-66 Comanche rotorcraft, the Lockheed Martin/Boeing F-22 fighter aircraft, and NASA's space station "Freedom". Of course, as the manufacturing methods become automated and material costs diminish, the use of fiber optics will become more attractive even for less demanding data communications applications e.g., the automobile industry.
The principle advantages of fiber optics include weight, material cost, and size when compared to a conventional twisted-shielded pair of copper wires. Firstly, for the same "data-carrying capacity", a fiber optic simplex cable weights about 0.0003% of the weight of a conventional twisted-shielded pair. For example, a ten-foot length of fiber optic cable having the capacity to transmit data at a rate of about 5.times.108 bps, weights about 0.009 kg. as compared to about 30.0 kg. for a copper wire bundle having the same data carrying capacity. Similarly, the material cost of the described ten-foot segment is about 0.07% of the cost associated with the comparable length of twist-shielded pairs. Moreover, the bundle diameter measures approximately 0.1586 cm. for the fiber optic cable verses about 12.7 cm. for the segment of twisted shielded pairs.
Yet additional advantages, particularly important to the aerospace industry, include protection against Electro-Magnetic Interference (EMI) and potential fire hazards. With respect to the former, conventional copper wiring used in aircraft is heavily shielded for preventing electromagnetic interference or "cross-talk" between systems. It will be appreciated that such protection is particularly important for aircraft flight critical systems, e.g., an Automatic Flight Control System (AFCS), wherein cross-talk between systems may introduce stray signals into the one of the flight critical systems. Fiber optic filaments, in contrast, are not electrically conductive, and, consequently, are immune to EMI. With respect to the latter, the electrical connections associated with conventional copper wiring can produce arcing, and, consequently, a spark which can be a potential fire hazard. It will be appreciated that in an aircraft carrying about 30% of its weight in jet fuel, the electrical connections must be highly protected/insulated and, preferably, positioned distally of fuel tanks/fuel lines. Fiber optic connections, in contrast, do not produce arcing, and, consequently, cannot become a source of ignition.
Despite the numerous advantages of fiber optics, several drawbacks persist with respect to the ruggedness/reliability of the fiber optic cable/termini, particularly when adapting fiber optics to a demanding operational environment. That is, it will be appreciated that the optical fiber employed in such cables is extremely delicate and prone to damage, especially when adapted for use in a high vibration and/or high temperature environment. For example, vibratory stresses can cause a minor imperfection, i.e., a small crack, introduced in the manufacturing process to propagate within the optical fiber and cause premature failure of the fiber optic cable. It will be appreciated that even small cracks in the optical fiber can seriously degrade or entirely defeat the transmission of data communication signals. Furthermore, elevated temperatures during the manufacturing process or, in its operational environment, can introduce thermal stresses in the optical fiber, which, similarly, can become the source of imperfections and failure of the optic fiber.
A need, therefore, exists to provide a fiber optic cable/terminus which is less susceptible to damage or signal degradation when adapted for use in a demanding operational environment, e.g., a high vibration and/or high temperature environment.